The invention, in some embodiments, relates to the field of electron beam emission and more particularly, but not exclusively, to methods and devices suitable for producing an electron beam.
In the 1990s, ferroelectric emitters for emitting electrons using polarization reversal were studied, see for example U.S. Pat. Nos. 5,453,661, 5,874,802 and EP 0428853B1.
In a typical example discussed with reference to FIGS. 1A and 1B, a film 10 (typically 1-10 micrometers thick, reported up to 100 micrometers thick) of ferroelectric material (such as PZT or PZLT) is sandwiched between a complete back electrode 12 and a perforated front electrode 14 (1-5 micrometers thick) including at least one small perforation 16 (˜10 micrometers diameter, ˜31.4 micrometer circumference), and a high transparency isolation grid 18 10-20 micrometers distally from front electrode 14 separated by a vacuum 20 (not greater than 10−3 Millibar).
For use, an AC power supply 22 is activated to apply a megahertz alternating current of up to ±100 V between electrodes 12 and 14 while a negative DC extraction potential of up to −200V) is applied to extraction grid 18.
When the phase of the current applied by power supply 22 is such that the potential on front electrode 14 is positive (FIG. 1A), ferroelectric film 10 is polarized in a direction 24a so that electrons accumulate at the bottom of hole 16 on the face of ferroelectric film 10.
When the phase of the voltage applied by power supply 22 is such that the potential on front electrode 14 is negative (FIG. 1B), ferroelectric film 10 is polarized in a direction 24b. The electrons accumulated in hole 16 on the face of ferroelectric film 10 are repelled into vacuum 20 to be extracted and accelerated by extraction grid 18 to form an electron beam.
Such ferroelectric emitters have been for the most part abandoned due to the very low current of electrons that these can produce.